search builder with aggregates support

Test is failing bc assertListEqual not defined?
```
Traceback (most recent call last):
  File "/home/travis/build/orchestrate-io/porc/tests/search.py", line 32, in test_aggregate
    self.assertListEqual(sorted(self.search.params['aggregate'].split(',')), sorted(expected.split(',')))
AttributeError: 'SearchTest' object has no attribute 'assertListEqual'
```